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How to wire? - Back fed Dry type 3 phase transformer - 240 to 440v

ggucci3

Plastic
Joined
Oct 11, 2021
I have built a RPC and recently got a 440v EMCO lathe that is rated for 4A. I have this dry type 9kva power transformer (image attached). I'm wondering:

1) Do I connect my 240v lines - l1, l2, l3 to x1 x2 x3 and leave x0 floating? If so, how do i run a safety ground to my machine?

2) There are three taps on each leg of the transfomer "output" H terminals (480v, 456v, 432v), Can I use this to my advantage to adjust my generated leg voltage? or should they all be connected to the same respective terminals?
3) I'm worried about the 208 low voltage side, my line voltage is actually 250v, so 16% higher than 208. not sure how much of an issue this is.. Can I wire 120 single phase to the transformer and then feed 480 single phase to my rpc?
 

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thermite

Diamond
I have built a RPC and recently got a 440v EMCO lathe that is rated for 4A. I have this dry type 9kva power transformer (image attached). I'm wondering:

1) Do I connect my 240v lines - l1, l2, l3 to x1 x2 x3 and leave x0 floating? If so, how do i run a safety ground to my machine?

2) There are three taps on each leg of the transfomer "output" H terminals (480v, 456v, 432v), Can I use this to my advantage to adjust my generated leg voltage? or should they all be connected to the same respective terminals?
3) I'm worried about the 208 low voltage side, my line voltage is actually 250v, so 16% higher than 208. not sure how much of an issue this is.. Can I wire 120 single phase to the transformer and then feed 480 single phase to my rpc?
"Personally..." I'd go and hunt-me-up a 220/230/240 to 440/460/480 .. "1:2" Delta-Delta transformer, instead of the Delta-Wye you have. You can get by with a considerably smaller one.

In reversing it for a Delta load, yes, you can ignore the "X0" Neutral-point of the Wye, yes, the 432 V tap is the one you want, BUT... 'even so'..

If your utility-mains service is, as mine is, 246 VAC into the 208 V winding, even with your lowest tap, it will probably be kicking out 511 VAC into the lathe.
About 16% over the nominal? That may or may not be OK?

On the other query:

- You cannot use the "re-derived" Neutral in the reversed mode, nor do you need it at the input side.

- Your PE ("Protective Earth" AKA "safety ground") is SEPARATE in any case. JFDI per standard practice on that one. Case, frame, chassis, "etc."
 
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